In this study the relationship of gamma-aminobutyrate (GABA) and its metabolism to biological aging is being investigated. The steady state concentration of the metabolites and enzymes of the GABA metabolic pathway is being determined in brain tissue of individual mice of known biological ages, including senescent. Specific inhibitors of purified brain glutamate decarboxylase and GABA-aminotransferase, enzymes that control the brain level of GABA, will be investigated. These specific inhibitors and compounds which either block or prolong the neurochemical action of GABA will be investigated as possible means of controlling the in vivo concentration of GABA in mice of different biological ages.